On Wed, May 20, 2015 at 9:25 AM, Jiri Olsa <[email protected]> wrote: > On Wed, May 20, 2015 at 03:52:09PM +0200, Peter Zijlstra wrote: >> On Wed, May 20, 2015 at 11:28:42AM +0200, Peter Zijlstra wrote: >> >> > --- >> > >> > c02cdbf60b51b8d98a49185535f5d527a2965142 is the first bad commit >> > commit c02cdbf60b51b8d98a49185535f5d527a2965142 >> > Author: Stephane Eranian <[email protected]> >> > Date: Mon Nov 17 20:07:02 2014 +0100 >> > >> > perf/x86/intel: Limit to half counters when the HT workaround is >> > enabled, to avoid exclusive mode starvation >> > >> > This patch limits the number of counters available to each CPU when >> > the HT bug workaround is enabled. >> > >> > This is necessary to avoid situation of counter starvation. Such can >> > arise from configuration where one HT thread, HT0, is using all 4 >> > counters >> > with corrupting events which require exclusion the the sibling HT, HT1. >> > >> > In such case, HT1 would not be able to schedule any event until HT0 >> > is done. To mitigate this problem, this patch artificially limits >> > the number of counters to 2. >> > >> > That way, we can gurantee that at least 2 counters are not in exclusive >> > mode and therefore allow the sibling thread to schedule events of the >> > same type (system vs. per-thread). The 2 counters are not determined >> > in advance. We simply set the limit to two events per HT. >> > >> > This helps mitigate starvation in case of events with specific counter >> > constraints such a PREC_DIST. >> > >> > Note that this does not elimintate the starvation is all cases. But >> > it is better than not having it. >> > >> > (Solution suggested by Peter Zjilstra.) >> > >> > Signed-off-by: Stephane Eranian <[email protected]> >> > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> >> > Cc: [email protected] >> > Cc: [email protected] >> > Cc: [email protected] >> > Cc: [email protected] >> > Link: >> > http://lkml.kernel.org/r/[email protected] >> > Signed-off-by: Ingo Molnar <[email protected]> >> >> OK, so if you have the watchdog enabled, that's 1 event, and having a >> max of 2 GP events, adding another 2 events is fail. >> >> Jiri, did you SNB have the watchdog disabled? > > watchdog was enabled > But maybe HT was disabled on your snb machine.
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